1. Field of the Invention
The invention relates to a trench gate type transistor and a method of manufacturing the same.
2. Description of the Related Art
A DMOS transistor is a double-diffused MOS field effect transistor and used as a power semiconductor device for a power supply circuit, a driver circuit or the like. A trench gate type transistor is known as a type of DMOS transistor.
This trench gate type transistor is configured by forming a gate insulation film 115 in a trench 114 formed in a semiconductor layer 112 and forming a gate electrode 116 covering the gate insulation film 115 in the trench 114 as shown in FIG. 27. A body layer and a source layer (not shown) are further formed in the front surface of the semiconductor layer 112 on the sidewall of the trench 114 by double-diffusion in the vertical direction.
A trench gate type transistor is described in Japanese Patent Application Publication Nos. 2005-322949, 2003-188379 and 2005-510087.
However, the conventional trench gate type transistor has problems that the gate capacitance (of the gate electrode 116, the gate insulation film 115 and the semiconductor layer 112) is large, the semiconductor layer 112 near the trench 114 easily has crystal defects, and the gate breakdown voltage is low due to gate electric field concentration.